1. Field of the Invention
The present invention relates to a pressure detector and a method of manufacturing the pressure detector.
2. Description of the Related Art
As an example of the prior art, US 2006/0162141A (corresponding to JP-A-2006-208043) discloses a method of manufacturing a pressure detector that can be suitably used for a combustion pressure sensor. The method includes steps of: preparing a first member including a sensing portion, a second member including a pressure-receiving diaphragm, and a pressure transmission member; inserting the pressure transmission member between the first member and the second member; monitoring an electric signal from the sensing portion, the electric signal corresponding to a preliminary load applied from the diaphragm to the sensing portion; determining the preliminary load on the basis of the monitored signal; and welding the first member and the second member in a state where the preliminary load is applied to the sensing portion.
In the above-described manufacturing method, even when the preliminary load is controlled to approach a predetermined value by monitoring the electric signal from the sensing portion, the preliminary load is difficult to be controlled with a high degree of accuracy due to a welding strain that is generated when the first member and the second member are welded.
The term “welding strain” means that at least one of the first member and the second member expands or contracts in a longitudinal direction of the first member and the second member due to increase or decrease of a volume of welding part of the first member and the second member. The preliminary load is a load that is applied from the first member and the second member to the pressure transmission member in a state where a pressure is not applied to the pressure transmission member from an outside of the pressure detector.
In a case where the welding is performed by using a laser beam, if an energy of the laser beam fluctuates, different welding strain is generated in each pressure detector due to a dimensional variation of the first member and the second member and a noise signal generated in a device for monitoring the electric signal from the sensing portion. Thus, the preliminary load of each pressure detector may vary.